Dental impression trays are used to create negative reproductions of a patient's teeth. These reproductions are generally used to cast models, for example, as is often required for making dental restorations such as crowns and bridges. To take an impression, the dental impression tray is usually filled with a flowable impression material, and then the tray is placed in the patient's mouth and pressed against the teeth. The impression material solidifies while the tray remains in the patient's mouth. As soon as the impression material has become solid, the tray is peeled away from the teeth and removed from the patient's mouth. Plaster or another flowable material is then poured into the solidified impression material to form the model of the patient's teeth.
Because the impression material flows around the teeth and then solidifies, it can be difficult to remove from the teeth even when significant force is applied to the tray. In some cases, the force applied to the tray separates the impression material from the tray rather than from the teeth, which means that the impression material must be separately peeled away from the teeth, and the accuracy required for dental impressions gets lost. This is inconvenient for the patient and the dentist because it tends to render the impression unusable, and as a result the procedure must be done again. The force required to separate the impression material from the tray should therefore be greater than the force required to separate the impression material from the teeth.
Traditionally, a dental adhesive is used to bond the dental impression material to the dental impression tray. Such dental adhesive can be, for example, a polyvinyl siloxane adhesive available from 3M ESPE AG, Germany under the designation VPS Tray Adhesive. The adhesive is first applied to the inner surface of the tray, where it must dry, typically for 3 to 6 minutes. Then the impression material is filled into the tray. Because in a dental practice time is often at a premium, it would be useful to reduce or eliminate the time required for adhesive application and drying if possible.
US 2003/0180680 discloses a dental impression tray comprising a retainer for the dental material. The retainer comprises loop-shaped anchoring elements which are connected to the inner surface of the tray. The retainer, for example, may be the loop part of a hook and loop mechanical fastener, or a non-woven textile material that is fixed to a surface of the tray. Impression material received in the tray is supposed to be anchored at the tray by the mechanical fastener as soon as the impression material has hardened.
U.S. Pat. No. 5,336,086 describes a dental tray having outer and inner walls and a base between the outer and inner walls. The outer and inner walls each comprise vertical slits having a shoulder within each slit, providing an interlock for the impression material that is squeezed through the slit. The base also has holes with a shoulder around the bottom side of each hole. Reservoirs associated with the holes are formed at the bottom of the base and surround the holes so that a relatively large amount of excess impression material that may be in the tray can flow through the holes into the reservoirs, and when solidified, retains the material when the tray is removed from a patient's teeth.
U.S. Pat. No. 7,021,929 relates to a dental impression tray having a plurality of projections and panels on its tray walls, all of which define grooves. Upon taking an impression, dental impression material flows into the grooves to form retentive components. These retentive components may prevent the impression material from distorting or being lifted out of the tray when the tray is disengaged from the teeth of the patient.
In EP 1 029 514 a dental impression tray is described as having an upper portion for holding the impression material, and a lower portion which is defined in the specification as “means for laterally displacing excess impression material.” The base of the upper portion has vent holes which force excess impression material to extrude toward the “means for laterally displacing excess impression material.” Excess material extruded from the holes interlocks with the excess material extruded from other nearby holes, thereby attaching the impression material to the tray. The tray further comprises a serpentine stop ridge which prevents the patient's teeth from contacting the base of the upper portion of the tray.
In DE 100 04 415 a dental impression tray with retaining elements for the impression material is disclosed. The retaining elements are integrally formed protrusions on a bottom portion of the tray. The retaining elements generally protrude in the direction from which the tray is pulled from a patient's teeth. To increase the retention force the retaining elements are supposed to provide, the protrusions are generally mushroom-shaped, meaning that they have an expanded free end.
Generally it takes some effort to manufacture dental trays with integrated retaining elements, because several manufacturing steps are often necessary. Furthermore, there is often a tradeoff between providing an effective retainer system, providing an easy-to-use tray and achieving inexpensive manufacturing.